1. Field of the Invention
The present invention relates to solid-state displacement elements based on a so-called xe2x80x9cintercalation phenomenonxe2x80x9d, optical elements to which such solid-state displacement elements are applied, and interference filters having solid-state displacement thin films which are fabricated based on the intercalation phenomenon.
2. Description of the Related Art
Research is being carried out diligently on displacement elements in which organic substances are inserted between layers of inorganic layered compounds having layered structures because it is expected that the displacement elements will bring about great advances in the highly advanced mechatronics field, such as for future intelligent robots and microelectronics. Herein, the layered structure refers to a structure in which layers, each composed of densely arranged atoms that are strongly bonded by covalent bonds and the like, are stacked in parallel by weak bonding forces, such as van der Waals"" forces, and the inorganic layered compound refers to an inorganic compound having such a structure. Such displacement elements are fabricated based on an intercalation phenomenon. Herein, the intercalation phenomenon refers to a phenomenon in which organic substances corresponding to electron donors or electron acceptors are incorporated or inserted between layers of an inorganic layered compound.
Conventional displacement elements or actuators can be classified according to the structure or the form thereof into, for example, eight groups, i.e., (1) piezoelectric ceramics, (2) polymer gels, (3) shape memory alloys, (4) hydrogen-storing alloys, (5) elements using fluid pressure, (6) electrostatic elements, (7) magnetostrictors, and (8) optical/piezooptical elements.
All of the above techniques are generally well known today. The most important physical properties of the displacement elements or the actuators include displacement (expansion and contraction), generated force, and response speed (control speed). If the above three characteristics can be simultaneously satisfied, that is, if an increase in displacement, an increase in generated force, and shortening of response speed are achieved, development of materials, devices, and various elements will greatly advance. However, under the existing circumstances, it is difficult to obtain displacement elements or actuators which simultaneously satisfy the three characteristics.
For example, although piezoelectric ceramics have excellent generated force and high response speed, the displacement (expansion rate) thereof is 1% or less. Currently, by combining the high-speed response thereof with ultrasonic techniques, ultrasonography, fish detectors, ultrasonic motors, etc. are practically used. However, examples using the displacement are limited to very few applications, such as high-precision actuators which are used for positioning probes of scanning tunneling microscopes (STMs) and atomic force microscopes (AFMs).
Although some polymer gels have a displacement (expansion rate) of several tens of percent to several hundreds of percent, the generated force thereof is significantly low and it is difficult to move heavy objects. Furthermore, it is not always easy to control expansion or contraction. Additionally, since the polymer gels are based on high polymers, the polymer gels are easily affected by heat and are greatly dependent on the operating environment.
Shape memory alloys recover their original shapes by heating after being deformed at low temperatures and, in principle, exhibit thermoelastic martensitic transformation. Therefore, although irreversible plastic deformation does not occur, high/low temperature controlling is required for the use thereof, and twin deformation by lattices is used, and therefore, a large displacement cannot be expected.
Although hydrogen-storing alloys are reversible, the hydrogen-storing alloys are based on the occlusion reaction due to the grain boundary diffusion of atomic hydrogen, thus being disadvantageous with respect to temperatures in the operating environment and responsiveness. Furthermore, the greatest challenge is elimination of heat of the reaction, and it is impractical to obtain small displacement elements or actuators.
Displacement elements or actuators which use fluid pressure are usually composed of composite materials including rubber and fibers, and are driven by air pressure or liquid pressure using the stretching properties thereof. Although such displacement elements or actuators are believed to be suitable for movement in analog form, it is difficult to perform micro-fabrication, and there remain problems with respect to the reduction in size and the integration of the displacement elements or the actuators.
Electrostatic elements are generally fabricated using the fine patterning processes which have been developed for silicon semiconductor devices, and the static electricity Coulomb force is used. Therefore, while the electrostatic elements are advantageous with respect to fine patterning of displacement elements or actuators, there remain problems with respect to the generated force. Furthermore, the greatest challenge is reliability, and because sliding units are included, deterioration easily occurs with time. The electrostatic elements are also easily affected by static electricity.
Magnetostrictors generally use a giant magnetostrictive effect, and materials having a strain of approximately 10xe2x88x923 at room temperature (e.g., Tbxe2x80x94Dyxe2x80x94Fe alloys) are known. The magnetostrictors have advantages with respect to displacement, generated force, small mass, etc. in comparison with piezoelectric elements. However, a serious drawback is that an external magnetic field is required for operating a magnetostrictor, and it is a challenge to provide a technique for forming a magnetic circuit in the vicinity of the magnetostrictor. In view of the above, it is difficult to reduce the size and increase the density of the magnetostrictors in comparison with voltage-driven piezoelectric elements.
As optical/piezooptical elements, for example, PLZT exhibiting a photovoltaic effect is known. In the optical/piezooptical elements, electromotive forces are produced by light irradiation based on pyroelectricity of the optical/piezooptical elements, and accordingly the inverse piezoelectric effect occurs, resulting in strain. Although noncontact operation is an advantage, since displacement is caused by inverse piezoelectricity through pyroelectricity, a large displacement cannot be expected, and poling treatment (voltage application) is required to induce displacement, thus giving rise to a problem in the process.
Preferably, displacement elements or actuators include constituents, all of which are solid state. Many organic substances are in a liquid state by themselves, and it is necessary to introduce them into solids without impairing the function of the organic substances. For that purpose, from the point of view of crystallography, it is best that a displacement element or an actuator has an organic molecule as a unit of a crystal structure. By employing such a structure, it is possible to completely prevent atoms and molecules from going in and out in response to the control of the displacement element or the actuator. In order to improve the generated force of the displacement element or the actuator, it is desirable that the displacement element or the actuator has a crystal skeleton similar to that of an inorganic compound. A so-called xe2x80x9cintercalation compoundxe2x80x9d simultaneously satisfies all the conditions described above, in which an organic substance is inserted (intercalated) between layers of an inorganic layered compound having a layered structure. The intercalation compound has both the toughness of the inorganic compound and the flexibility of the organic substance, and is a material which is similar to a biological muscle.
Solid-state displacement elements or actuators using intercalation compounds have been known, for example, from Japanese Unexamined Patent Application Publication Nos. 5-110153, 6-125120, 2-131376, and 4-127885.
In the solid-state displacement element disclosed in Japanese Unexamined Patent Application Publication No. 5-110153 or 6-125120, external electrodes are provided, and an electric field generated by applying a voltage to such electrodes is applied to an intercalation compound in which an organic substance is inserted into a layered compound, and the alignment angle of the inserted organic substance is changed, and thus the displacement element is displaced. However, since the electric field must be applied from outside in order to displace the displacement element, the construction of the means for forming the electric field becomes complex, which is disadvantageous. In the above two unexamined patent application publications, no mention or suggestion is made with respect to techniques for controlling the displacement and operation of the solid-state displacement elements based on light.
Japanese Unexamined Patent Application Publication No. 2-131376 discloses an actuator which includes graphite intercalation compound layers as expansion portions, and the expansion or contraction of the expansion portions is used for producing shape displacement. Specifically, cubical expansion resulting from the intercalation phenomenon is used as a driving force, and intercalants between the graphite intercalation compound layers are electrically and thermally added or removed, and resulting expansion and contraction of the graphite intercalation compound layers are used to construct the actuator. Japanese Unexamined Patent Application Publication No. 4-127885 also discloses an electrochemical actuator, in which cubical expansion resulting from the intercalation phenomenon is used as a driving force. Specifically, a compound oxide containing Ag0.7V2O5 and vanadium oxide is used as positive/negative poles, 4AgIxe2x80x94Ag2WO4 is used as a silver-ion conductive solid electrolyte, and at least one of the poles exhibits a reversible volumetric change in response to an electrochemical oxidation-reduction reaction.
However, in the above two unexamined patent application publications, no mention or suggestion is made with respect to solid-state displacement elements which use a change in the state of organic substances inserted between inorganic layered compounds as a driving force or with respect to techniques for controlling the displacement and operation of the solid-state displacement elements based on light.
Accordingly, it is an object of the present invention to provide a solid-state displacement element in which displacement (expansion and contraction) can be caused by a very simple method or construction, an optical element using such a solid-state displacement element, and an interference filter provided with a solid-state displacement thin film in which displacement (expansion and contraction) can be caused by a very simple method or construction.
In accordance with the present invention, a solid-state displacement element includes an inorganic layered compound having a layered structure and an organic substance inserted between layers of the inorganic layered compound. When controlling light is irradiated, the solid-state displacement element expands or contracts in the lamination direction of the inorganic layered compound.
In accordance with the present invention, an optical element includes an inorganic layered compound having a layered structure and an organic substance inserted between layers of the inorganic layered compound. When controlling light is applied to the optical element, the optical element expands or contracts in the lamination direction of the inorganic layered compound, thus modulating the polarization of transmitted light passing through the optical element.
Preferably, the transmitted light passing through the optical element enters substantially in the lamination direction of the inorganic layered compound constituting the optical element, and is linearly polarized.
In accordance with the present invention, an interference filter includes a multilayered film composed of a dielectric material and a solid-state displacement thin film disposed between layers of the multilayered film. The interference filter transmits or reflects light in a predetermined wavelength region. The solid-state displacement thin film includes an inorganic layered compound having a layered structure and an organic substance inserted between layers of the inorganic layered compound. When controlling light is applied to the interference filter, the solid-state displacement thin film expands or contracts in the lamination direction of the inorganic layered compound, and a dielectric constant tensor thereof changes, and thus the wavelength region of light passing through or reflected from the interference filter changes.
The solid-state displacement thin film may be disposed between layers of the multilayered film or on an outermost surface of the multilayered film. The number of the solid-state displacement thin film disposed between layers of the multilayered film is not limited to one, and at least two solid-state displacement thin films may be disposed.
In the solid-state displacement element, the optical element, or the interference filter (hereinafter sometimes referred to as xe2x80x9cthe solid-state displacement element or the likexe2x80x9d) of the present invention, preferably, the organic substance is composed of an organic compound in which the arrangement in the solid-state displacement element or the like can be changed in the direction of an electric field of the controlling light, and the solid-state displacement element or the like expands or contracts in the lamination direction of the inorganic layered compound in response to variations in the arrangement of, for example, a main chain of the organic compound. In such a case, preferably, the controlling light is applied to the solid-state displacement element or the like in a direction substantially perpendicular to the lamination direction of the inorganic layered compound. However, the incident angle of the controlling light entering the solid-state displacement element or the like is not limited to substantially perpendicular. Herein, xe2x80x9csubstantially perpendicularxe2x80x9d means that the incident angle of the controlling light toward the solid-state displacement element or the like is not necessarily strictly perpendicular. Alternatively, when controlling light which is linearly polarized is applied to the solid-state displacement element or the like in the direction substantially perpendicular to the lamination direction of the inorganic layered compound, the solid-state displacement element or the like preferably expands or contracts in the lamination direction of the inorganic layered compound depending on the direction of the electric field of the linearly polarized light. That is, preferably, the expansion state of the solid-state displacement element or the like is varied by changing the direction of the electric field of the linearly polarized light in the controlling light applied to the solid-state displacement element or the like.
Alternatively, in the solid-state displacement element or the like of the present invention, preferably, the organic substance is composed of an organic compound in which the molecular structure or the conformation can be changed depending on the wavelength of the irradiated controlling light, and the solid-state displacement element or the like expands or contracts in the lamination direction of the inorganic layered compound in response to variations in the structure or the conformation of the organic compound. In such a case, preferably, when controlling light having a first wavelength (for example, a. wavelength of less than 500 nm) is applied to the solid-state displacement element or the like, the solid-state displacement element or the like expands or contracts in the lamination direction of the inorganic layered compound to be in a first expansion state, and when controlling light having a second wavelength (for example, a wavelength of 500 nm or more) is applied to the solid-state displacement element or the like, the solid-state displacement element or the like expands or contracts in the lamination direction of the inorganic layered compound to be in a second expansion state that is different from the first expansion state, in which the solid-state displacement element or the like remains in the first expansion state until the controlling light having the second wavelength is applied to the solid-state displacement element, and the solid-state displacement element or the like remains in the second expansion state until the controlling light having the first wavelength is applied to the solid-state displacement element or the like, namely, the solid-state displacement element or the like may be provided with a memory function. Depending on the organic substance, when the controlling light is applied to the solid-state displacement element or the like, the solid-state displacement element or the like expands or contracts in the lamination direction of the inorganic layered compound to be in the first expansion state, and when the controlling light is not applied to the solid-state displacement element or the like, the solid-state displacement element or the like expands or contracts in the lamination direction of the inorganic layered compound to be in the second expansion state that is different from the first expansion state. Additionally, the controlling light may enter the solid-state displacement element or the like in any direction, and for example, the controlling light may be applied to the solid-state displacement element or the like in a direction substantially perpendicular to the lamination direction of the inorganic layered compound.
In the solid-state displacement element or the like of the present invention, preferably, the organic substance is composed of at least one organic compound selected from the group consisting of an organic compound having at least one of an aliphatic carbonxe2x80x94carbon bond, an aromatic ring, and a heterocyclic ring, in which at least a part of hydrogen atoms directly bonded to any one of carbon atoms may be replaced by nitrogen or sulfur, and an organic compound in which at least a part of hydrogen atoms directly bonded to carbon atoms constituting a carbon compound is replaced by nitrogen or sulfur. More preferably, the organic substance is composed of at least one organic compound selected from the group consisting of a chiral liquid crystal, a phenylpyrimidine-based liquid crystal, a phenylpyridine-based liquid crystal, an amine-based liquid crystal, a biphenylpyrimidine-based liquid crystal, an azobenzene-based compound, a porphyrin-based compound, an anthraquinone-based compound, a spiropyran-based compound, a diarylethene-based compound, a stilbene-based compound, a fulgide-based compound, urea [CO(NH2)2], and carbon disulfide (CS2). Alternatively, more preferably, the organic substance is composed of an organic compound in which the conformation or the molecular structure can be changed. Alternatively, preferably, the organic substance is composed of an organic compound having a polar functional group. More specifically, the organic substance is preferably composed of an organic compound in which at least one polar functional group (e.g., xe2x80x94NH2, xe2x80x94NR2, xe2x80x94NPh2, and xe2x80x94SO3H) is bonded to at least one of carbon atoms constituting the organic substance, wherein R is an alkyl group, and Ph is a phenyl group.
In the solid-state displacement element or the like of the present invention, examples of the organic compound in which the arrangement in the solid-state displacement element or the like can be changed in the direction of an electric field of the irradiated controlling light include a chiral liquid crystal represented by the chemical formula 1 below, a phenylpyrimidine-based liquid crystal represented by the chemical formula 2 below, a phenylpyridine-based liquid crystal represented by the chemical formula 3 below, an amine-based liquid crystal represented by the chemical formula 4 below, and a biphenylpyrimidine-based liquid crystal represented by the chemical formula 5 below. 
On the other hand, examples of the organic compound in which the molecular structure or the conformation can be changed depending on the wavelength of the irradiated controlling light include an azobenzene-based compound represented by the chemical formula 6 below, a porphyrin-based compound represented by the chemical formula 7 below, an anthraquinone-based compound including quinizarine represented by the chemical formula 8 below, a spiropyran-based compound including spirobenzopyran represented by the chemical formula 9 below, a diarylethene-based compound including diarylethene represented by the chemical formula 10 below, a stilbene-based compound represented by the chemical formula 11 below, and a fulgide-based compound represented by the chemical formula 12 below. Additionally, a change in the molecular structure or the conformation means that photoisomerization occurs between a cis-form and a trans-form due to optical pumping, or that a new combination occurs or a combination splits in a molecule due to light irradiation. 
In the solid-state displacement element or the like of the present invention, the inorganic layered compound, or the inorganic layered compound as a starting material before the organic substance is inserted between the layers, may be composed of at least one inorganic layered compound selected from the group consisting of a layered perovskite-type niobium-based compound, such as KLaNb2O7, KCa2Nb3O10, RbCa2Nb3O10, CsCa2Nb3O10, or KNaCa2Nb4O13; a layered perovskite-type copper-based compound, such as Bi2Sr2CaCu2O8 or Bi2Sr2Ca2Cu3O10; a layered titanoniobate, such as KTiNbO5, K2Ti4O9, or K4Nb6O17; a layered rock salt-type oxide, such as LiCoO2 or LiNiO2; a bronze-based compound in a transition metal oxide, such as MoO3, V2O5, WO3, or ReO3; a transition metal oxychloride, such as, FeOCl, VOCl , or CrOCl; a layered polysilicate, such as Na2Oxe2x80x944SiO2xe2x80x947H2O; a layered clay mineral, such as smectite, vermiculite, or mica; a hydrotalcite, such as Mg6Al2(OH)16CO3xe2x80x94H2O; a transition metal chalcogenide, such as TaSe2, TaS2, MoS2, or VSe2; a zirconium phosphate, such as Zr(HPO4)2nH2O; and graphite. Additionally, the various compounds described above may have compositions that slightly deviate from stoichiometric compositions.
In order to generate the controlling light, any means may be used, for example, a laser.
Among the three important factors, i.e., displacement (expansion and contraction), generated force, and response speed (control speed), which are required for the solid-state displacement element, the optical element, or the interference filter, in particular, the present invention has a great advantage with respect to the generated force and the response speed. That is, in order to improve the generated force, the inorganic layered compound having the layered structure is used, and the superior response speed can be achieved because the organic substance inserted (intercalated) between the layers of the inorganic layered compound sensitively responds to the controlling light irradiated from outside. Moreover, since the expansion and contraction of the solid-state displacement element, the optical element, or the interference filter are controlled by light irradiation, the control system can be simplified.